Metal articles and materials for making same



METAL ARTICLES AND MATERIALS-FOR MAKINGSAME James B. Russell, Davenport, 'Iowa, assignor to Kaiser a -corporation of Delaware I No Drawing. Filed Feb. 25, 1957, Ser. No.-641,821

16 Claims. "(CL 29-1961) i'Tliis invention relates to composite metal articles having a ferrous metal base. portion coated with a particular aluminum' base alloy, the process for producing such composite articles and the aluminum base coating alloys. More particularly, the invention relates to aluminum alloys particularly adapted for the hot dip coating of a composite metallarticle.

Coatings of aluminum on iron and steel products are .highly desirable, since the composites resulting in eifect embody the superior properties resident in each metal.

To the strength and other desirable.characteristicslof the iron .orsteel 'core,' the aluminum coating adds the more salient properties of resistance'to corrosion and oxidation atboth atmospheric and elevated temperatures,'enhanced electrical conductivity, improvement'inuthe facility of Patent No. 2,782,493, directed to other particular..;aluminum base, coating alloys and the composite metal articles produced therewith, it has been discovered that superior results may be obtained with certain aluminum base alloys asthe coating material inre'gard tosuch factors as the appearance and continuity of the coating, and the ductility of .the composite metal article compared with aluminum coated ferrous base composites utilizing high purity aluminum or commercially pure aluminum (28 alloy).

a s ted M 2,1961

. appearance and continuity'of 'the coating .in regard to become of primary importance. 7

coatingof rigid or semi-rigid articles such as castings coverage, smoothness, texture, luster and other factors For example, in the and the like, wherein batch or semi-continuous processes jot-coating are in general employed, appearance and con- ,tinuity of the coated-composite are 'thef foremost factors .Aluminum 8: ChemicalCorporation, Oakland, Calif.,

, ferrous metal base, thehot dip process and the resulting to be consideredj Ductility is relatively unimportant 1 since the article in its coated form is not'subjecte'd'to any extensive; deformation or subsequent working operations.

Other specific examples of such articles are" forgin'gs,

stampingsand other shaped semi-finished or finished ferrous base articles.

Of the several processes "forthe production of alum-- num coated 'ferrous base composite articles, the hot dip method is the most desirable. from 'an economic standpoint and from the standpoint of rangeof applicability. However, the production of aluminized (aluminumcoated) ferrous base metal articles byrneans of the advantageous hot dip method, to'which the present invention is particularly directed, has presented many problems.

In regard to the hot. dip process, other factors in addition to appearance and continuity of the coating and ductility of the composite are involved. ,These' are primarily the molten bath operational characteristics, such as apparent fluidity,- wettability of the ferrous base metal with the I molten aluminum bath, forming rate, 'thickness v tenacitybf-the oxide 'film on the. molten .bath surface,

f herence, in the as-coated condition.

which principally influence those characteristics oftlie coating determining appearance and continuity, such as coverage, smoothness, 'texturefand luster, aswell as ad- As indicated in. my copending applications above r'effe'rred to, .diffi'culty has been encountered inthe use of high purity or commercially pu're aluminum in'the hotdip coating of ferrous metal articles in regard to the inability 'toiobtain composite articles having the requisite ductility.

Thisfproblem has been circumvented by the addition of certain alloying constituents which have effectively reduced the "thickness and hardness of the intermetallic iron aluminum layer which forms between the basis metal and the coating alloy. Thus, aluminum base'alloys eminent-1i With regard to the results obtained with aluminum base alloys of a' given composition, theprimary factor tobe considered is the intended use or'purpos'e of the com-- posite article being produced, For example, in the fabrication of aluminum coated ferrous base metal products, it is often necessary that the composite article exhibit the ability to withstandhigh 'degrees of deformation upon erations 'mustpossess good ductility so that thecoating.

suitable for coating Wrought productsfsuch as wire and strip have been developed wherein the composite article produced may be subjected'to subsequent formingoperations withoutjcracking or spalli'ngof the aluminum base alloy coating. However, high purity. or commercially pure aluminum. as the coating'materials for ferrous, metal articles by, the hot dip' process" also exhibit definite delici; encies in regard. to the appearance of the coatings produced with respect to suchfactorsaifectingf appearance as adherence, and continuity of'the coating, smoothness,

coverage, texture and even luster. In mosti'nstances the appearance of high purity is poor due to the large grains will not crack and break away,' that is, peel-or flake off'efrom the base metal during the subsequentworkin g In addition, the adherence of thealurninum coating to the ferrous metalbase is involved'in regard to the required characteristics that the coating=will not peel'or spall; ,Also" freedom from tendency of theco'atingfto crack'durin'g subsequentoperations or in service is neces 1 visible'andanmarked grain boundary depression in the surface, Withcbmm erc'ially pure aluminum (28 alloy),

the large grainfstru'cture tends to persist while 'the ceat ings are relatively 'dull due to "an opaque oxide film;

Also,'particular'difiicu1ty has been encountered withfh'ot' dip coatings on castings wherein there .has been apronounced inability to'produce coatings where coverage is 11 complete, that 'is,.continuity of the coating is lacking;

sary so as to avoid any "exposure ofthe base metalto I corrosion,- :The combination of.excellent ductilityrchar acteristies iof thecomposite, and adherence of the coating together with excellent appearance of the-coatingis the. objective attained With'the particular aluminum gbase ala'ife directed .loys to which the above referred tocopending applications "Infin ty-instances, however, therefatecert'ain end uses 1 or; purposjes fqr alu'rninu 'n coatedff 'errousf base rnetala, v afticles -iniwhich d'uctilityi relatively unimportant; and

" co r tinuity of hotdip aluminumalloycoatings on ferrous base metal articles that the present invention is particuregard to smoothness, texture and luster.

and moreover the coatings are often of poorqualityfin It is to this problem relating to the appearance and larity directed.

' It is, therefore, primarypurpose and object of invention ,to providev hot 'dip aluminum alloy coated ferrous base, metalja 'riticles which {exhibit excellent ap et te,

ance and continuity ofthe coatings in'rega'r'd to coverage} ticular aluminum base alloys adapted for the hot dip coating of ferrous base metals characterized by improved wettability of the ferrous metal base and their ability to form coatings and composite articles exhibiting excellent properties of adherence of the coating, and appearance and continuity of the coatings in regard to brightness,

smoothness, coverage,fand substantial absence of undesirable visible large grain surface effect.

It is a more specific object of the .present invention to provide aluminum alloys for coating ferrous metal where- 'in the appearance and continuity factor including such properties as coverage, smoothness, texture and luster of the coating are of paramount importance and ductility of the composite is not a significant factor, which aluminum :base coating alloys are superior in regard to the abovev mentioned properties of the coating compared to high purity or commercially pure aluminum as a coating material.

It is a further object of the invention to provide a method of hot dip coating ferrous metal with particular aluminum base alloys to produce coatings on composite articles having the desirable combination of properties above-mentioned while operating at advantageous temperatures in regard to minimizing the thickness of the intermetallic alloy layer and without any substantial ad- A verse effect on the operational characteristics of .the molten coating metal. A specific object is to provide particular aluminum base alloys as coating material for semi-rigid and rigid ferrous metal articles, such ascastings, wherein excellent i'appearance of the coating is obtained in regard to the factors including adherence, coverage, smoothness, continuity, texture and luster thereof.

These and other objects and advantages of the invention will be apparent from the following detailed description thereof.

It has been discovered according to the invention that hot dip aluminum coatings on ferrous base metal of improved appearance in regard to coverage, continuity,

smoothness, texture and luster compared to high purity r s 4 posite article produced is relatively unimportant. In regard to ductility, however, it must be noted that the alloys of the present invention produced composites which upon subjection to 180 flat bend tests and spiral wrap tests exhibited ductilities which were at least comparable to and in some cases better than the ductilities of composites utilizing high purity or commercially pure aluminum.

The elements chromium, molybdenum and tungsten generally may be present in amounts of from about 0.1

to about 0.40% each, the total not exceeding about 0.5%. The preferred range is from about 0.15 to about 0.25% each of these elements, and in general, as noted above, it is preferable to employ only chromium and molybdenum, or chromium and tungsten, and not all three of the elements, although the latter polynary alloy is definitely included within the scope of the invention, since, for example, lesser amounts of molybdenum may be employed and tungsten added to the chromium-molybdenum alloy, although when all three elements are present it is still preferred not to substantially exceed a total of about 0.5%.

As a further feature of the invention, it was discovered that the appearance of the above-defined ternary and more complex aluminum base alloys could be still further improved by the addition of at least one, and preferably only one, of the elementss boron, titanium, vanadium and zirconium. Of these elements, titanium is the preferred species, although all of the named elements contribute to a marked improvement in the appearance of the coating alloys of the invention by markedly increasing the smoothness of the alloy coating and rendering the surface appearance more uniform and of even luster. In addition, an improvement in the ductility of the alloy coating was noted with small but etfective additions of these elements. The visible grain, marring the appearance of high purity aluminum and 28 alloy coatings, was eliminated by the presence of one or more of these elements.

The element boron as one of the above group produces the advantages above noted, and, in addition, may be advantageously used to reduce bumpiness sometimes occurring in the coatings and to effect a general smoothing action on the coating.

Additions of boron and titanium are recommended in amount from about 0.02 to about 0.2% by weight of the alloy. The preferred range of these elements is from about .02 to .05% B and 0.02 to 0.1% Ti. When used to- V gether the preferred total is about 0.06%. The other two least one of the elements molybdenum and tungsten, preferably only one of the last two named elements being utilized, to produce the above-mentioned desired results. It 'is to be noted that molybdenum is the preferred constituent to be added to the chromium-containing aluminum alloy, but that tungsten may be used more or less intersmoother in surface texturein comparison with coatings,

produced by high purity aluminum and commercially pure aluminum (25 alloy). In addition, the chromium constituent of the aluminum base alloy coating increased the attractiveness of the color and luster of the coating in solid form on the ferrous base. i

L The coating alloys of the present invention provide remarkable results in regard to adherence, continuity, coverage and smoothness of, coatings applied to cast fer rous metal articlese and" are accordingly eminently suitr able for utilization'in the hot dip process wherein. appearanoe is the primaryfactorand ductility of the con elements, namely vanadium and zirconium are recommended in amount from about 0.1 to about 0.25%. Although single additions of these elements are preferred, theyv may be used collectively, particularly where only two such elements are employed. In any event, the total where vanadium and zirconium are used collectively should not exceed about 0.5

It has also been found according to the invention that very limited or small amounts of beryllium have a desirable'effect on the appearance of the coatings This element'exhibits the ability to reduce the amount of surface oxide on the molten aluminum alloy coating bath. The use of beryllium is particularly advantageous when coating with aluminum alloys containing silicon or sodium. Brown oxides are formed on the bath surface when these elements are incorporated in the molten coating alloy and cause staining of the coating. Amounts of from about 0.001 to 0.015% of beryllium are very effective in preventing the formation of this stain due to the brown oxide, and at the same time do not have any adverse effect on the ductility of the coating. A preferred lower amount of about 0.002% beryllium is recommended.

The use of beryllium in these amounts is to bdistinguished from the use of beryllium in larger amounts where it functions similarly tosilicon inhavingatprb .deiinite'counteracting ,eirectlin .lthis l regard. .Amounts of molybderium+0.06% titanium;

"02%molybdenum. I v I 1 The aluminum .alloys"of fthednvention iembrace those houn'ced intermetalliclayer thickness redueing effect. f In :any event, beryllium-as anoptional element -in the coat-v f ing alloys ofthe present -inventionfor improvement in the appearanceofthe composite is limited" to-arnounts below 0. 02 and"amounts-substantially in excess "of this jvalue are required to provide a decrease in the thickness ef inter-metalliclayer and resulting improvement ductility.

where beryllium is-addedto the molten aluminum coating alloy bath, additions aremadeperiodically to replace that lo'stthrough*oxi'da'tiorrand'due to chlorine flux- "ing, when 'the blatterimethod is employed. These addi- Qtions arer-made {preferablyby adding aluminum-5% "beryllium hardener to maintain the composition at the desired "beryllium content in the alloy.

R has beenffoundthat'thealloysfof the present invention may also; advantageously "contain an additional constituent; namely; Zing-Which contributes along with. chi-o fmium 'and"molybclenurn"to anincrease in the surface I. 1

brightness. or luster .of the coatingand the attractive color thereof. Ina'd'dition the zinc constituentjalso' contributed to'an improvement in appearance-of thelcoating'by its beneficial effect on. ,thecontinuity thereof. 1 In general,

additions of zinc'jinamountsfrom abQutfOLS to about 2% by weight of, the total-alloy composition werefound to he ,efiectivenin this regard. The preferred range for ,zinclis jfrom about 026 .to .about "11%,, sincef in some 'in stances coatings containing as high as 2%,.Zinq exhibited ,atendency towardgatspangling effect on'l'fthesurface of 1 "coating,,althoughfthe; presence of onerofithet elements rthe s' mlpincluding.ii anium set forth abovehad ,a

lzineas high 'as 2% iri somefinstances tended to decrease fiuidi-tylof t-he melt, although not. to .a disqualifying extent.

{Ihe zinc 'nconstituent aa-lso appears 7 to -contribute to the cathodic; protection 1of the, ferrous.base particularly where =the;.base would "become zex-posedrdueto any cracking of p .theLaluminum basej-alloy coating during use, of. the composite article. i

; ;Ihe. a-lloying constituents- 0f thefpresentainvention ex-. .erte a;benecial;eflect;on t-he;operationalcharacteristics of the; uminum i-melt by improvedwettability to the ferrous base. Eurther; they exerted nocadverse effect. in regard to such-[factors has apparent: fluidity, oxide forming. rate, oxide thickness ;and jtena'city; intthe molten. state. In fast, in certain instances the oxideaforming'rate,aoxide'thickness wand oxide stain, the "formercharacteristic judged qualitatively,. werevreducediiby the:pre sence"ofcertain of .the{ alloying 'constitutents of the present invention, notably heryllium'gas set 'forth -above. a

staiiding appearanee infthe as coated condition relative to the reference alloys, tnainely 99i9% aluminum and comrriercially pure -a1uminum (2 5 alloy) the following 'may be mentioned: (1 0.2% chromium-41% zinc 0.2%molybdejnum-.07%g titanium; (-2) 0.2%] chromiu rn-0.2%

coating materials whichmay'be designated as'the ter nary a andjrnore complex alloys set forth above wherein the hal 'anceof thelalloy is. substantiallygall aluminum a'nd'im-fl purities in normalamounts; The term impurities -innor. mal amounts. as used herein and in the. appended claims includes ;theiron which may be progressiveiyj picked up by the molten aluminum alloy bath 'from the ferrous base the-v alu minumcoating metalu I The aluminum base alloys may be a prepared by adding. the addition elements to themolten -aluminum bath: in elemental forrrr or' 'in suitable compound form. Preferably,

hot dip process various procedural modifications may be employed. However, since these alloys are particularly intended for utilization in coating ferrous metal articles wherein the composites produced are more or less semifinished or finished articles, the process most advantageously employed is the batch or semi-continuous: process. Of course. the invention is not to be regarded aslimited to-theparticular manner in which the aluminumalloy coating is applied to'the ferrous base by'the hot'dip method and in many instances the continuous process may be employed for coating wire and stripmaterials wherein: ductilities comparable to those of high purity and coinmercially pure aluminum coated composites are acceptable. In either case, the coating alloys and molten bathsprepared therefrom produce aluminum alloy coated ferrous metal articles superior in appearance and continuity to similar articles coated with high purity aluminum and commercially pure aluminum, and far superior to articlesproduced 'by the utilization of alloy coating'materials. p

The ferrous articles to be coated are first thoroughly cleaned by any suitable method; such asacidpickling to remove oxide film or scale unless the surface condition renders this treatment unnecessary. -They may then be aluminum-silicon binary rinsed and dried, and immersed injthe coating bath with' or without the use of aconventional flux. On the-other hand, the articles withor without pickling depending upon:

- the nature of the-surface may be pretreated by bright annealing in suitable apparatus in an inert 'or'reducing atmosphere and then directly immersed in the molten coating bathwithout exposure to the atmosphere.

The bath temperature is maintained sufiiciently high so thatthe alloys employed are completely molten. 'Of' course, the particular bath temperature depends upon thecoating alloy composition and the composition andnature. of the ferrous article; and in regard to the alloys herein disclosed temperatures of from about 1250 to about 'l375 "F. are recommended. Since thickness of the Fe'-Alinterfacial layer increases with bath temperatime; it is recommended that the lowest operating temperature consistent with good coating results be used.

.The, time of immersion depends principally upon thecomposition .of the molten bath,ithe, composition and recommended 1 nature;,of the ferrous-article, and the temperature of the molten bath. -The immersion time and'also the bath: temperature maybe regulated. to :produce a. composite most suitable forztheintended application. Extending the time ,of immersion .tends to increase the thickness of thezFe'Al layerand accordingly the shortest immersion times iconsistent with satisfactory coverage are usually fExantple Y iXs'anexampl'e'of one specific procedure in utilizing the coating materialsofthe invention to produce corn-" posites by the hot dipme'thod; the following isiset forth a's illustrative without cons'tituting a limitation on ithe scope-ofthe-disclosure-and.claimsappended heretoz i' Specimens consisting of*--m'ild*-steel strip containing 0.2% manganese -and-less thanO. 1 carbon, 12 inches in length, inch wide and .036 inch thick wereused. All I specimens were 'degr'eased with' carbon tetrachlorideand ,wiped dry with cloth, then pickled 'in.a:;40% -HCl-solution for from 15 to 25 seconds at 'aft'emperature'r ef '7 160 F. This was followed by a water rinse and the cleaned specimens were dried with gauze.

The specimens were then dipped in a molten bath of aluminum base alloy containing 0.2% chromium-0.2% molybdenum and 0.06% titanium, the balance aluminum and less than 1% normal impurities. Identical specimens were dipped in molten baths of 99.9% aluminum, commercially pure aluminum (2S alloy) and a 5% siliconaluminum binary alloy. No fiuxes were employed, and the specimens were immersed for from to seconds with the bath temperature maintained at about 1300 F. The coated specimens were withdrawn and tapped lightly while in a vertical position to facilitate removal of ex- .cess coating.

The surfaces of the specimen coated with 99.9% aluminum were mottled in appearance due to the visible large grain structure of the coating and the coverage of the coating at the edges of the strip tended to be incomplete, or where continuous it was rough.

The coating of commecially pure aluminum (28 alloy) was also characterized by a visible large grain, which, however was somewhat obscured by a more or less opaque .oxide film which presented a relatively dull appearance compared to a metallic luster. The coating on the edges .ofthe strip was rough and continuity was slightly lackv The 5% silicon-aluminum alloy coating had a dull greyish color seriously lacking in luster, and was characterized by a markedly rough surface texture over substantially the whole strip, although the coating was continuous on the strip edges.

, The strip coated with the alloy of the invention had a uniform, pleasing luster and was exceptionally smooth in texture with complete coverage even at the edges. No objectionable large grain was visible on the surface of the coating.

Accordingly, the alloys of the invention as coating materials for ferrous base metals produce composites of improved appearance and continuity as evidenced by the excellent coverage, smooth grainless texture and luster of the coatings compared to conventional high purity and commercially pure aluminum coatings, and vastly improved appearance as contrasted with the aluminumsilicon alloys.

It is to be noted that during the course of continued operation either on the batch'or continuous basis, the molten aluminum alloy bath gradually increases in iron content due to pickup by dissolution of iron from the basis metal. Small amounts of iron in the coating alloy, up to just below saturation, for example, 2.5% at the usual coating temperatures, may be tolerated without any significant adverse effect on-the character of the coating and composite. However, when the iron content increases to, for example 3 or 4%, it exceeds the saturation point (on the liquidus line) depending upon the particular coating temperature and composition of the bath, and begins to affect quality of the coatings and composites, particularly in regard to smoothness. Various procedures may be adopted for reducing the iron content'and increasing effective bath life among which may be mentioned discontinuance of operation of the bath while permitting the heavy iron component to settle out of the molten aluminum alloy, or addition of fresh amounts of unicontaminated aluminum alloy to effectively reduce the concentration of iron in the total molten bath. 7 Of course,

' What'is claimed is: a

1. A composite article comprising a base portion 0 ferrous metal hot dip coated with an aluminum base alloyof improved wettability to the ferrous base consisting essentially of chromium in amount from about 0.1 to 0.4%, and at least one of the elements molybdenum and tungsten in amount from about 0.1 to 0.4%, the total amount of these alloying constituents not exceeding about 0.5%, the balance substantially all aluminum and impurities in normal amounts. p 2. A-composite article according to claim 1 in which the aluminum base alloy contains also at least one element selected from the group consisting of boron, titanium, vanadium and zirconium in amounts from about 0.02 to about 0.2% boron and titanium, and about 0.1 to about 0.25% vanadium and zirconium, the total of these elementsnot exceeding about 0.5%. 3. 'A composite article according to claim 1 in which the aluminum alloy also contains zinc in amount from about 0.5 to about 2%.

, 4. A composite article the aluminum alloy also 0.02% beryllium.

5. A composite article the aluminum alloy also 0.02% beryllium.

6. A composite article the aluminum alloy also 0.02% beryllium.

7. A composite article the aluminum base alloy contains also at least one eleaccording to claim 1 in which according to claim 2 in which contains from 0.001 to below according to claim 3 in which contains from 0.001 to below ment selected from the group consisting of boron, titanium, vanadium and zirconium in amounts from about 0.02 to about 0.2% boron and titanium, the total of boron and titanium not exceeding about 0.06%, and about 0.1 to about 0.25% vanadium and zirconium, the total of vanadium and zirconium not exceeding about 0.5%.

8. A composite article according to claim 7 in which thealuminum alloy also contains from 0.001 to below 0.02% beryllium. t

9. A hot dip coated product comprising a ferrous metal base coated with an aluminum base alloy consisting essentially of from about 0.15 to about.0.25% chromium, and one element selected from the group consisting of molybdenum and tungsten in amount from about 0.15 to about 0.25 balance substantially all aluminum and im purities in normal amounts.

10. A composite article according to claim 9 in which the aluminum base alloy contains also one element selected from the group consisting of boron, titanium,

- vanadium and zirconium in amounts from about 0.02 to from about 0.6 to about 1%.

employing a new bath of aluminum alloy obviatesthe problem, but is a less desirable solution wtih regard to treating a maximum amount of ferrous base metal with a minimum aluminum alloy consumption.

All percentages in the claims are by weight of the 12. ,A composite article according to claim 9 in which the aluminum alloy also contains from 0.002 to 0.015% beryllium. I 1

13. A composite article according to claim l0'in.which the aluminum alloy also contains from 0.002 to 0.015% beryllium. a I 14. A composite article according to claim 11 in which the aluminum alloy also contains from 0.002 to 0.015% beryllium; a I f '15." A composite article according to claim,11 in which the alur'ninumbase alloy contains also one element Selected from the group consisting of boron, titanium, vanadium. and zirconium in amounts from about 0.02 to abou 0.05% boron, from about .05 to 0.1% titanium and about 0.1 to about 0.25% vanadium and zirconium.

' 16. A composite article according to claim 15 in which the coating alloy contains from 0.002 to.0.015% beryl:

(References.onfollowingpage).

contains from 0.001 to below according to claim 3 in which References Cited in the file of this patent 2,280,174 Stroup Apr. 21, 1942 UNITED STATES PATENTS 2,357,450 1 014 BP 5, 194 1,663,150 Archer Mar. 20, 1928 OTHER REFERENCES 1,850,355 Russell Mar. 22, 1932 5 Effect of Bath Compqsition Coating on Steel, Gittings 2,091,419 Schroeder Aug. 31, 1937 et al., preprint published October 1950, ASM, 19 pages.

. UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,982,015 May 2, 1961 James B. Russell It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 7, after "improvement" insert in llne l, for "fast" read fact column 8, line 55, after "aluminum" lnsert base line 55, for from 0,002 to O,Ol5% read zinc in amounts Signed and sealed this 17th day of October 1961,,

(SEAL) Attest:

Commissioner of Patents Attesting Officer USCOM M-DC 

1. A COMPOSITE ARTICLE COMPRISING A BASE PORTION OF FERROUS METAL HOT DIP COATED WITH AN ALUMINUM BASE ALLOY OF IMPROVED WETTABILITY TO THE FERROUS BASE CONSISTING ESSENTIALLY OF CHROMIUM IN AMOUNT FROM ABOUT 0.1 TO 0.4%, AND AT LEAST ONE OF THE ELEMENTS MOLYBDENUM AND TUNGSTEN IN AMOUNT FROM ABOUT 0.1 TO 0.4%, THE TOTAL AMOUNT OF THESE ALLOYING CONSTITUENTS NOT EXCEEDING ABOUT 0.5%, THE BALANCE SUBSTANTIALLY ALL ALUMINUM AND IMPURITIES IN NORMAL AMOUNTS. 